Just an update guys...
If you look at the original boxes for your cartridges you might find that they are 23/24 (Black/Colour) and are not refillable (well physically they are, but they won't work as the printers are "chipped" to reject them). The boxes are likely to be red.
I tried to buy generic cartridges which are refillable, but I couldn't get them anywhere. The only solution seems to be to buy Lexmark cartidges 33/34 Black/Colour), these boxes are grey. These cartridges are a little bit more expensive but they are refillable.
Another point to note is that these cartridges are only primed to give on average less than 500 pages, so if you are a heavy print user it can work out cheaper to have documents photocopied commercially!!
It really galls me

that most shops only sell the non refillable cartridges as they make more money out of the repeat purchases!! and when you do buy cartridges the sellers don't make it their business to tell you the cartridges are not refillable, but once bitten twice shy!!
Hope this helps some of you guys avoid he same mistake I made.
Noel